Clamping telescopic tubes

ABSTRACT

Clamping method and apparatus for an outer tube and an inner tube telescopically disposed within the outer tube, the apparatus being normally concealed from view and having a threaded coupling member mounted in one end of the inner tube, an anti-rotate loop carried by the coupling member and an expandable lock which opens against the inside surface of the outer tube and closes in response to axial displacement of the threaded coupling member. The anti-rotate loop firmly contacts the interior surface of the outer tube and is displaceable over the surface along the axis of the outer tube. Relative rotation of the inner and outer tubes causes the anti-rotate loop to bind against the inside surface of the outer tube to rotate the threaded coupling member relative to the inner tube thereby spreading the lock tightly against the inside surface of outer tube until further rotation of tubes as well as relative axial displacement are prevented.

United States Patent Kirkham 1 July 4,1972

[54] CLAMPING TELESCOPIC TUBES 22 Filed: March 16,1970

21 Appl.No.: 19,581

Primary Examiner-Andrew V. Kundrat Attorney-Lynn G. Foster [57] ABSTRACT Clamping method and apparatus for an outer tube and an inner tube telescopically disposed within the outer tube, the apparatus being normally concealed from view and having a threaded coupling member mounted in one end of the inner tube, an anti-rotate loop carried by the coupling member and an expandable lock which opens against the inside surface of the outer tube and closes in response to axial displacement of the threaded coupling member. The anti-rotate loop firmly contacts the interior surface of the outer tube and is displaceable over the surface along the axis of the outer tube. Relative rotation of the inner and outer tubes causes the anti-rotate loop to bind against the inside surface of the outer tube to rotate the threaded coupling member relative to the inner tube thereby spreading the lock tightly against the inside surface of outer tube until further rotation of tubes as well as relative axial displacement are prevented.

8 Claims, 13 Drawing Figures PKTENTEDJUL 4 I972 3. 674.294 SHEET 2 or 3 INVENTOR.

ARTHUR J. KIRKHAM ATTORNEY CLAMPING TELESCOPIC TUBES BACKGROUND 1. Field of the Invention The present invention relates generally to clamping and more particularly to methods and apparatus for securing a selected telescopic relation of tubes with clamp structure which is concealed from view.

2. The Prior Art Conventionally, tent poles and the like comprise at least two separable pole segments which can be attached in an axiallystaggered relation to form a single pole structure having a fixed length. Tent poles of this type are frequently awkward to handle, thus often making tent erection a difi'rcult and timeconsuming procedure. 7

It is also known to use telescoping tubes, as tent poles. In erecting a tent, the telescoped tubes are normally set to the desired length by relatively displacing the inner tube with respect to the outer tube followed by closing of an exteriorly exposed, conventional clamp structure. Historically, the desired position maintained by the exteriorly exposed clamping structure selectively bites into the exterior surface of the inner tube, fits within slots or the like in the inner tube or extends through openings in the outer tube. Such clamping structure disadvantageously scores and defaces the exterior of the inner tube so that an unsightly appearance results, materially weakens the inner tube when slots are used and is inefficient in that an opening selected may not cause the tent covering to be taut. Also, frequently such clamping structure is easily bumped or otherwise inadvertently released causing all or part of the tent to collapse.

BRIEF SUMMARY AND OBJECTS OF THE INVENTION According to the present invention, the axial position of telescoping tubes can be maintained by clamping structure which is concealed from view and acting internal of the outer tube so that scoring and other defacement of visible portions of the tubes is avoided. Also, the combined length of the inner and outer tubes is securely adjustable to essentially any desired telescopic length without risk of inadvertently releasing the secured adjustable position of the tubes. The methods and apparatus of this invention require an anti-rotate feature which allows for the changing of the effective length of the clamping structure within the tubes to spread a lock to tightly hold the two poles in the desired relative position against relative rotational and axial displacement.

It is a primary object of the present invention to provide novel clamping structure for telescopic tubes or poles.

It is another primary object of the present invention to provide improved methods for setting the axial relation of telescoping tubes.

These and other objects and features of the present invention will become more fully apparent from the following description and appended claims taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an exploded perspective view of one presently preferred embodiment of the invention;

FIG. 2 is an assembled perspective illustration of the clamping structure of FIG. 1, parts being broken away to reveal the relationship of the clamping structure to the outer tube;

FIG. 3 is a longitudinal cross section taken along line 3-3 of FIG. 2;

FIG. 4 is a cross sectional view similar to FIG. 3, FIG. 4 illustrating the clamp in the closed position;

FIG. 5 is an exploded perspective of another presently preferred embodiment of the invention;

FIG. 6 is a fragmentary perspective illustration of the clamping structure of FIG. 5, parts being broken away to reveal the relationship of the clamping structure with the outer tube;

FIG. 7 is a cross section taken along line 7-7 of FIG. 6;

FIG. 8 is a cross section similar to FIG. 7 illustrating the engaging position of the clamping structure;

FIG. 9 is an exploded perspective view of another presently preferred embodiment of the invention;

FIG. 10 is a fragmentary perspective illustration of the clamping structure of FIG. 1 with parts broken away to reveal the relationship of the clamping structure with the outer tube;

FIG. 1 1' is a longitudinal cross section taken along line 11- l 1 of FIG. 10;

FIG. 12 is a cross section similar to .FIG. 11 illustrating the clamping structure in the engaged position; and

FIG. 13 is a fragmentary perspective view illustrating still another presently preferred embodiment of the invention,

.parts being broken away to reveal the relationship of the clamping structure with the outer tube.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS I Figures 1-4 With reference particularly to FIGS. 1-4, the illustrated clamp, generally designated 20, is preferably mounted upon the upper end 22 of a hollow elongated pole or tube 24, the cross sectional configuration of which. can be of any desired type although a circular configuration is illustrated. If desired, a solid pole with an axially disposed blind bore would be used. A cylindrical insert 26 has a diametral dimension which is essentially the same as the inside diametral dimension of the tube 24. Insert 26 has a flat upper surface 28 and an axiallydirected through-bore 30, which is interiorly threaded. A circumferential groove or indentation 32 is disposed in the cylindrical insert 26 around the entire curved periphery of the insert at essentially mid-length. Insert 26 is normally disposed into the interior 34 of the tube 24 until the upper surface 28 is flush with the end 22 of the tube 24. Preferably, the insert 26 is secured in the mentioned flush relation by crimping or swedging the tube 24, as at 36 (FIG. 2), to tightly secure the insert 26 in place and thus prevent both axial and rotational relative movement of the insert 26 and the tube 24.

An annular bearing ring 38 is normally superimposed upon the surface 28 and an annular washer 40 having a central aperture 42 is carried upon the bearing ring; 38. The washer 40 has radially directed grooves 44 which are oppositely disposed at the aperture 42. Each groove 44 tapers upwardly and outwardly, and terminates essentially midway between the aperture 42 and the peripheral edge of the washer 40. Grooves 44 serve a function subsequently more fully described.

An exteriorly threaded linking shaft 46 is, in the assembled condition, disposed through the aperture 42 in the washer 40, the ring 38, and is threadedly secured in the through-bore 30 of insert 26. The threaded shaft 46 has an axial slot 48 which opens at the top end 50 and terminates in an abutment surface 52 located a substantial distance from the top end 50 of the shaft 46. A generally U-shaped expandable jaw or lock 54, which may be formed of heavy gauge resilient wire, is normally disposed within the slot 48. Lock. 54 has a rounded base 56 and upwardly and inwardly directed arms 58 and 60. The arms terminate in outwardly directed free ends 62 and 64. In the assembled condition illustrated in FIG. 2, base 56 of the lock 54 rests upon the surface 52 in slot 48 so that the ends 62 and 64 project outwardly away from the threaded shaft 46.

Transverse apertures 66, disposed in each of the two bifurcated ends of the shaft 46 near the end 50, are adapted to snugly receive a keeper or pin 68. Keeper 68 serves as an axle for spreader 70. Spreader 70 is generally disc-shaped and is provided with an axial bore 72 through which the keeper 68 is normally disposed. As best shown in FIGS. 2-4, when the spreader 70 and keeper 68 are properly assembled, the circumference of the spreader 70 is disposed adjacent the neck portion 65 of the lock 54.

Keeper 68 is also disposed through apertures 74 in the lower end 76 and 78 of the two legs of a resilient anti-rotate loop 80.

The anti-rotate loop is preferably formed of resilient steel ribbon and, in the assembled condition illustrated in FIGS. 2-4, is normally non-rotatably secured to the threaded shaft 46 by the keeper 68. The anti-rotate loop 80 has outwardly-directed yieldable skis 82 and 84 and tapers upwardly to joint 86 where the members are secured together such as by welding or by a rivet 88. The yieldable nature of the skis 82 and 84 allows clamp 20 of a given size to be used with tubes of varying sizes.

In the at-rest position, the distance between the skis 82 and 84 is preferably slightly greater than the inside diameter of the outer tube 90. Outer tube 90 is disposed over the anti-rotate loop 80 by forcing the loop into the tube 90 thereby squeezing the skis 82 and 84 together to shorten the distance between skis 82 and 84 and increase the distance between the joint 86 and the top end 50 of shaft 46. The memory of the anti-rotate loop 80 will cause the skis 82 and 84 to forcibly engage the interior surface 92 of the outer tube 90 as shown in FIG. 2.

Referring now to FIGS. 3 and 4, the method of axially fixing the relative positions of the inner and outer tubes 24 and 90, respectively, will be described. In the initial relatively axially displaceable condition illustrated in FIG. 3, the threaded shaft 46 is situated relative to the insert 26 so that the abutment surface 52 is flush with or beyond the top surface of the washer 40. The connecting portion 56 of the lock rests upon the abutment surface 52 and the ends 62 and 64 are held, due to the memory of the lock 54, inward of and free from engagement with the inside surface of the outer tube 90, the ends 62 and 64 being situated adjacent the spreader 70.

The anti-rotate loop 80 is laterally compressed within and exerts an outward force directed through the skis 82 and 84 (FIG. 2) against opposed portions of the interior surface 92 of tube 90. The tube 24 is inserted into the tube 90 easily by merely exerting a force generally along the axis of tube 24 toward the tube 90 and a counter force along the axis of tube 90. The skis 82 and 84 allow the loop 80 to readily slip axially along the interior surface 92.

When the selected telescopic relation between tubes 24 and 90 has been reached, so as to effect a desired combined effective length of the tubes 90 and 24, the tubes 90 and 24 are relatively oppositely rotated. While relative opposite rotation of tubes 24 and 90 is easily accommodated, the edges of the skis 82 and 84 of the anti-rotate loop 80 bind upon the interior surface 92 and prevent rotation of the loop 80 and the shaft 46 relative to the tube 90. Thus, the shaft 46 turns with the tube 90 relative to the tube 24 and insert 26, when the two tubes are oppositely rotated. Relative opposite rotation in one way will lock the clamp 20 while relative opposite rotation in the other way will unlock the clamp 20, as hereinafter more fully explained.

When the tubes are relatively oppositely rotated so that the threaded shaft 42 is retracted into the insert 26, the connecting portion 56 of the lock 54 will become seated in the grooves 44 of washer 40 (see FIG. 4). Continued retraction of the shaft 46 will cause the spreader 70 to exert a downward force between the ends 62 and 64 at the neck portion 64 thereby spreading the ends outwardly into tight engagement with the interior surface 92 of the tube 90. See FIG. 4. When the ends 62 and 64 are so engaged, relative axial displacement of the tubes 90 and 24 is prohibited.

When desired, the tubes 24 and 90 may be relatively oppositely rotated in an opposite manner to advance the threaded shaft 46 up out of the insert 26 and the memory of the material forming the lock 54 will cause the ends 62 and 64 to be retracted out of engagement with the surface 92. Thereafter, facile relative axial displacement of the tubes 24 and 90 may be attained.

Figures -8 FIGS. 5-8 illustrate another presently preferred clamp structure of the invention, generally designated 93, which, in some respects, is similar to the embodiment of FIGS. 1-4, like parts being designated with like numerals throughout. Specifically, an insert 94 has a frusto-conical upper end 96 which tapers upwardly to top abutment surface 98. The insert 94 has an exterior peripheral surface which is adapted to mate with the interior 34 of the inner tube 24. A peripheral groove 100 existing around the entire exterior circumference of the insert 94 allows the insert 94 to be swedged or otherwise fixed in the tube 24 as described relative to insert 26, above.

A generally U-shaped lock 102, preferably of spring steel, has a connecting base 104 and upwardly directed flat arms 106 and 108, which converge at a neck portion 109. Arms 106 and 108 have outwardly turned ends 110 and 112, respectively.

A centrally located aperture 114 disposed in the connecting portion 104 of the lock 102 is axially aligned with a threaded bore 116 in the insert 94. The threaded shank 118 of a bolt 120 is normally loosely disposed through the aperture 1 14 and threadedly secured in the threaded bore 116. The bolt 120 has a head 122 which serves to spread the ends 1 10 and 112 of the lock 102 and has a transverse through-bore 124 disposed therein. Keeper 68 is normally disposed through the bore 124, keeper 68 having a length which is greater than the transverse dimension of the head 122.

An anti-rotate loop 126, preferably of ribbon spring steel, has an inverted generally U-configuration with downwardly directed ends 128 and 130. The ends 128 and 130 have apertures 132 and 134, respectively, which are rotatably or nonrotatably secured to the head 122 by the keeper 68. The antirotate loop 126 is preferably resilient and yields or flattens when forced into any one of several tubes of diverse sizes which causes opposed lateral forces to be exerted on the sides 136 and 138 of the loop 126. Thus, the outer tube 90 may be superimposed over the clamp structure 93 by flattening the anti-rotate loop 126 at sides 136 and 138 and, thereafter, axially forcing the tube 90 telescopically over the clamping structure 93 and part of the tube 24.

The mode of operation of the clamp structure 93 is similar to the mode of locking and unlocking of the clamp structure 20, above-described. Because the connecting base 104 rests upon the surface 98 of insert 94, axial retraction of the threaded shank 118 into the insert 94, in response to relative opposite rotation of the two tubes in one manner, will cause the lock 102 to spread as the arms 106 and 108 above the neck portion 109 are forced outwardly by the head 122 of bolt 120. The anti-rotate loop 126 non-rotatably couples the loop 126 and the bolt 120 to the tube 90 and prevents the bolt 120 from rotating with the inner tube 24 as the tubes 24 and 90 are relatively oppositely rotated. When the ends 110 and 112 of the lock 102 tightly engage or bite the interior surface 92 of tube 90, as shown in FIG. 8, the relative axial positions of tube 90 and tube 24 are fixed and an overall effective length for the two tubes is established. Relative opposite rotation of the tubes in an opposite manner will release the locked condition, substantially as earlier described in respect to FIGS. l-4.

Figures 9-12 The clamp structure of FIGS. 9-12, generally designated 104, comprises an insert 142 having an elongated cylindrical body portion 144 and a planar upper surface 146. The insert 142 has a peripheral groove 148 which serves the same function as groove 32 in insert 26 (FIG. 1).

An elongated axially-disposed slot 150 laterally spans the insert 142 and, therefore, opens at opposed sides of the insert. As best shown in FIGS. 11 and 12, the bottom 152 of the slot 150 has a central recess 154 with surrounding ridges 156 and 158. Lock 54, described in connection with FIGS. 1-4, above, is situated in the slot 150 so that the connecting base 56 rests in the recess 154 between the ridges 156 and 158.

The insert 142 is oriented within the tube 24 so that the slot 150 is in direct communication with opposed apertures 160 and 162 fabricated in the tube 24. The apertures 160 and 162 are spaced from the end 22 of the tube 24 so that when the insert 142 is properly secured within the tube 24, the ends 62 and 64 of jaw 54 are respectively directly opposite and partially within the apertures 160 and 162.

With continued reference to FIGS. 11 and 12, the insert 142 has an axially-directed internally threaded bore 164 which opens to the top exterior of the insert 142 at surface 146 and which also opens into the slot 150. Bore 164 receives the threaded shank 166 of bolt 168 in mating relation. Bolt 168 is illustrated as having a square head 170 with a through-bore 172 which communicates to opposed flat sides of the head 170.

The anti-rotate loop 126, described relative to FIGS. 5-8, above, is secured to the head 170 with keeper 168 in bore 172. In the assembled relation illustrated in FIG. 10, only. the antirotate loop 126 and the bolt 168 project above the end 22 of tube 24 into the tube 90.

To axially lock the tubes 90 and 24 in a desired telescopically-fixed relation with the clamping structure 140, the lock 54 is displaced fromthe at-rest position of FIG. 11 to the locked condition of FIG. 12. In the at-rest position, the lower end of the threaded shank 166 of bolt 168 is disposed out of contact with the lock 54. However, the lock 54 is maintained in the upright position shown by the relatively narrow width of slot 150, by the ridges'154 and 156 and by the ends 62 and 64 being situated in the apertures 160 and 162.

As the tubes 24 and 90 are oppositely relatively rotated in one of two possible ways, the shank 166 of bolt 168 will be retracted into the insert 142 until the lower end of the shank 166 engages the lock 54 between ends 62 and 64 near the neck portion 65. As shown in FIG. 12, continued retraction of the bolt 168 into the recess 150 will spread the ends 62 and 64 and cause them to project outwardly through the apertures 160 and 162 into biting engagement with the interior surface 92. When the ends 62 and 64 firmly bite into the surface 92, relative axial displacement of the tubes 24 and 90 is prevented. Relative opposite rotation of the tube in the other way will cause unlocking of the lock 54 due to return of the clamp structure 140 to the condition of FIG. 1 1.

Figure 13 FIG. 13 illustrates still another presently preferred clamping structure, generally designated 176. The clamping structure 176 comprises a bolt 178 having a threaded shank 180 which is threadedly secured into the threaded bore 30 of insert 26, previously described. The bolt 178 is illustrated as having a spherical spreader head I82 situated between the ends 184 and 186 of the lock 188.

Lock 188 is generally U-shaped in configuration, made of material with memory and has an aperture (not shown) in the connecting base 192, through which the shank 180 of bolt 178 is loosely disposed. In the at-rest position, the ends 184 and 186 are situated adjacent the spreader head 182 of bolt 178.

A resilient anti-rotate loop, generally designated 194, is formed of resilient ribbon steel and has a centrally disposed aperture 196 which loosely circumscribes the shank 180 of bolt 178 near the head 182. Significantly, the anti-rotate loop 194 is welded to the shank 178 at the aperture 196 so that relative rotation between the bolt 178 and the anti-rotate loop 194 is prohibited.

Loop 194 has ends 198 and 200 which overlap one another adjacent the connecting base 192 of lock 188. Each end 198 and 200 is provided with an essentially identical elongated slot 202 through which the bolt 17 8 loosely passes.

In the compressed condition, such as when the anti-rotate loop 194 is disposed within the outer tube 90, the ends 198 and 200 move inwardly relative to one another against the natural bias of the loop 194 to allow the loop 194 to be compressed or flattened sufficiently to be inserted into the outer tube 90. The memory of the material from which the loop 194 is fabricated continuously urges the loop outwardly against the interior surface 92 of the tube 90 so that as the tube 90 and tube 24 are relatively oppositely rotated, the bolt 178 will be rotated with the tube 90 relative to the tube 24.

In the mode of locking tubes and 24 together against relative axial displacement using the clamping structure 176, it can be appreciated that relative opposite rotation of the tubes 24 and 90 in one way will cause the bolt 178 to be threadedly retracted within insert 26. The spreader head 182 will be forced between the ends 184' and 186 of lock 188 thereby forcing the ends 184 and 186 into biting engagement with the interior surface 92 of tube 90. Reverse opposite relative rotation of the tubes will unlock the mechanism 176 in the manner earlier explained.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

l. Clamping structure comprising means for carrying the clamping structure at one end of one elongated member sized and shaped to fit within an open end of another generally hollow elongated member, yieldable anti-rotate means having relatively fiat bearing surfaces formed with relatively sharp edges for generally axial insertion into and snug non-rotatable engagement with the interior surface of the hollow elongated member,

lock means movable between an unlocked position and a locked position contiguous with the interior surface of the hollow elongated member and having relatively shar surface-engaging portions for biting engagement with said surface to prevent relative axial movement of the elongated members, and

means carried by said anti-rotate means and responsive to relative opposite rotation of the elongated members to cause the lock means to move between the two mentioned positions.

2. In combination,

a male pole,

a female pole, telescopically related to the male pole, and

clamping structure, the clamping structure comprising means for carrying the clamping structure at one end of the male pole,

yieldable anti-rotate means with memory formed with relatively flat skidding surfaces having relatively sharp edges for generally axial insertion into and snug non-rotatable engagement with the interior surface of the female pole,

lock means movable between an unlocked position and a locked position contiguous with the interior surface of the female member and having relatively sharp surface-engaging portions for biting engagement with said surface to prohibit axial movement of one pole with respect to the other pole, and

means carried by said anti-rotate means responsive to relative opposite rotation of the poles to cause the lock means to move between the unlocked and locked position.

3. Clamping structure for selectively preventing axial movement of one tube relative to another tube, the one tube having an inner end normally telescoped into the other tube, the improvement comprising:

linking means carried by the one tube near the inner end,

which linking means are displaceable relative to the one tube when the one tube and linking means are relatively rotated;

yieldable resilient means mounted upon the linking means and having relatively flat tube-engaging surfaces formed with relatively sharp edges accommodating axial movement of the linking means relative to the inside surface of the other tube and resisting rotational movement of the resilient means relative to the other tube; and

expandable means expanded by displacement of the linking means relative to the one tube for selectively biting into the inside surface of the other tube to thereafter prevent relative axial displacement of the one and other tubes.

4. Structure as defined in claim 3 wherein the expandable means comprise resilient jaw means having a generally U- shaped cross section with free ends adapted to bite into the interior surface of the outer tube when the jaw means are open.

5. Structure as defined in claim 3 wherein said resilient means comprises a deformable loop attached to the linking means and adapted to be disposed within the outer tube, the loop having ski means formed with relatively flat tube-engaging surfaces accommodating axial displacement of the loop relative to the outer tube, said surfaces having relatively sharp edges which bind against the inner surface of the outer tube to resist rotational relative displacement therewith when a rotational force is exerted upon the deformable loop.

6. Structure as defined in claim 5 wherein said linking means comprises a threaded shaft threadedly secured to the inner end of the one tube and having an axial slot therein into which the expandable means is disposed, and a bearing plate disposed at the inner end of the one tube upon which the expandable means are supported for relative movement with the one tube and a spreader-disc carried by the threaded shaft within the axial slot so that as the threaded shaft is advanced through the bearing plate, the expandable means will engage the spreader-disc and be forced outwardly into biting engagement with the other tube.

7. Structure as defined in claim 3 wherein said expandable means are U-shaped and comprises an aperture at the bottom thereof and wherein said linking means is a threaded shaft having an enlarged head, the shaft being disposed through the aperture and into a threaded bore in the inner end of the one tube so that the ends of the U-shaped means are disposed adjacent the enlarged head and are outwardly projected thereby when the threaded shaft advances into the inner tube.

8. Structure as defined in claim 3 further comprising a cylindrical insert adapted to be rigidly mounted in the inner end of the one tube, the insert comprising an axially elongated transverse slot into which the expandable means are disposed; and axial bore communicating the transverse slot with the exterior of the insert, the bore receiving linking means so that as the linking means are selectively advanced into the insert, the expandable means are forced outwardly through opposed apertures in the inner end of the one tube into engagement with the other tube. 

1. Clamping structure comprising means for carrying the clamping structure at one end of one elongated member sized and shaped to fit within an open end of another generally hollow elongated member, yieldable anti-rotate means having relatively flat bearing surfaces formed with relatively sharp edges for generally axial insertion into and snug non-rotatable engagement with the interior surface of the hollow elongated member, lock means movable between an unlocked position and a locked position contiguous with the interior surface of the hollow elongated member and having relatively sharp surface-engaging portions for biting engagement with said surface to prevent relative axial movement of the elongated members, and means carried by said anti-rotate means and responsive to relative opposite rotation of the elongated members to cause the lock means to move between the two mentioned positions.
 2. In combination, a male pole, a female pole, telescopically related to the male pole, and clamping structure, the clamping structure comprising means for carrying the clamping structure at one end of the Male pole, yieldable anti-rotate means with memory formed with relatively flat skidding surfaces having relatively sharp edges for generally axial insertion into and snug non-rotatable engagement with the interior surface of the female pole, lock means movable between an unlocked position and a locked position contiguous with the interior surface of the female member and having relatively sharp surface-engaging portions for biting engagement with said surface to prohibit axial movement of one pole with respect to the other pole, and means carried by said anti-rotate means responsive to relative opposite rotation of the poles to cause the lock means to move between the unlocked and locked position.
 3. Clamping structure for selectively preventing axial movement of one tube relative to another tube, the one tube having an inner end normally telescoped into the other tube, the improvement comprising: linking means carried by the one tube near the inner end, which linking means are displaceable relative to the one tube when the one tube and linking means are relatively rotated; yieldable resilient means mounted upon the linking means and having relatively flat tube-engaging surfaces formed with relatively sharp edges accommodating axial movement of the linking means relative to the inside surface of the other tube and resisting rotational movement of the resilient means relative to the other tube; and expandable means expanded by displacement of the linking means relative to the one tube for selectively biting into the inside surface of the other tube to thereafter prevent relative axial displacement of the one and other tubes.
 4. Structure as defined in claim 3 wherein the expandable means comprise resilient jaw means having a generally U-shaped cross section with free ends adapted to bite into the interior surface of the outer tube when the jaw means are open.
 5. Structure as defined in claim 3 wherein said resilient means comprises a deformable loop attached to the linking means and adapted to be disposed within the outer tube, the loop having ski means formed with relatively flat tube-engaging surfaces accommodating axial displacement of the loop relative to the outer tube, said surfaces having relatively sharp edges which bind against the inner surface of the outer tube to resist rotational relative displacement therewith when a rotational force is exerted upon the deformable loop.
 6. Structure as defined in claim 5 wherein said linking means comprises a threaded shaft threadedly secured to the inner end of the one tube and having an axial slot therein into which the expandable means is disposed, and a bearing plate disposed at the inner end of the one tube upon which the expandable means are supported for relative movement with the one tube and a spreader-disc carried by the threaded shaft within the axial slot so that as the threaded shaft is advanced through the bearing plate, the expandable means will engage the spreader-disc and be forced outwardly into biting engagement with the other tube.
 7. Structure as defined in claim 3 wherein said expandable means are U-shaped and comprises an aperture at the bottom thereof and wherein said linking means is a threaded shaft having an enlarged head, the shaft being disposed through the aperture and into a threaded bore in the inner end of the one tube so that the ends of the U-shaped means are disposed adjacent the enlarged head and are outwardly projected thereby when the threaded shaft advances into the inner tube.
 8. Structure as defined in claim 3 further comprising a cylindrical insert adapted to be rigidly mounted in the inner end of the one tube, the insert comprising an axially elongated transverse slot into which the expandable means are disposed; and axial bore communicating the transverse slot with the exterior of the insert, the bore receiving linking means so that as the linking means are selectively advanced into the insert, the expandable means are forced outwaRdly through opposed apertures in the inner end of the one tube into engagement with the other tube. 